The invention relates to an electrical connector and, more particularly, a card edge electrical connector having pull-through, press-fit bellows type contacts in an insulator removable from around the contacts following rigid mounting of the contacts to a mounting substrate.
Historically, prior art electrical connectors have been assembled by very tightly press fitting or molding contacts into receiving blocks of insulative material which form structural members to support the contacts and hold them rigidly within the insulative body. The prior art connector having contacts rigidly fixed within the insulator, are then mounted by bolting the insulator to a pair of spaced parallel rails, or by dropping the contact tails into holes in a mounting substrate and soldering them in place. Problems have arisen in substrate mounted connectors of this type in that generally the insulator forms the structural member which supports the contacts and the insulator cannot be removed after the connector is mounted to the substrate. Further, it is virtually impossible to remove individual ones of such prior art contacts from within the insulator and/or the mounting substrate in the event one of the contacts is damaged.
The prior art techniques for assembly of the aforesaid connectors are also relatively slow because of the time required to rigidly mount each individual contact into its receiving sleeve within the insulator. Certain prior art connectors have overcome this problem by providing for simultaneous insertion of rows of contacts held together on stips into receiving sleeves which hold them in position within the insulator. Simultaneous contact insertion greatly speeds the connector assembly process and the generally light insulator/contact holding force typical of such assemblies enables insertion of the contacts into the insulator by hand, eliminating the need for mechanical pressing apparatus. Such contact-insulator assemblies are oftentimes typical of the connectors which are press fitted into contact receiving apertures in a mounting substrate. Such a connector is set forth and described in U.S. Pat. No. 4,220,393 entitled "Electrical Connector and Method of Fabrication and Assembly" and assigned to the assignee of the present invention. Likewise issued U.S. Pat. No. 4,045,868 issued Sept. 6, 1977 and assigned to the assignee of the present invention and entitled "Method of Fabrication and Assembly of Electrical Connector", sets forth and describes one method of providing a press fit electrical connector in the manner set forth above.
A trend in the development of the substrate mounted connector art is that of using structures which permit the removal of the insulator from mounted contacts. Certain prior art discrete connectors have included insulators adapted for tightly holding top loaded contacts in sleeves formed therein and, in certain instances, have been used as the seating tool for press fitting the contacts in this configuration. Such an approach is illustrated in U.S. Pat. No. 3,530,422, to David S. Goodman, entitled "Connector and Method for Attaching Same to Printed Circuit Board". The connector described in the Goodman Patent, includes contacts having transverse shoulder portions which are top loaded down into slots in the insulator. The contact tails are pulled through to seat the contacts, and the lower shoulder portion of each contact is twisted 90 degrees to lock each contact into the insulator bottom with the relatively large outwardly extending shoulder of the contact. The contacts can then be press fitted into apertures in a substrate by applying a force to the top of the insulators. Once the contacts have been press fitted, it is impossible to remove the insulator to expose individual ones of the contacts for repair. Similarly, each of the contacts are locked into the insulator to permit its individual removal therefrom.
In many prior art discrete connector assembly operations, the contacts are loaded into the insulator with requisite force for preliminarily securing the contacts therein and then a pulling force is applied to the bottom tail of the contacts relative to the insulator to seat the contacts securely therein. Such "pull-home" forces are generally substantially equivalent to the "push-out" force of the contact in the insulator and require additional tooling to effect the pull-home operation. Most pull-home fixtures are adapted for engaging and pulling contacts one at a time rather than in a series. Such an operation is both time consuming and imparts higher cost to the assembly. It may also be observed that when the connector of certain of these discrete assemblies is mounted upon a printed circuit board, the contact may be designed to be removed for purposes of repair. In such connectors, the contact push out force thereof is generally equivalent to the push-in force due to the type of mating configuration. However, the push-in force is optimally as low as possible to eliminate deformation of any of the components during assembly, and, therefore, the push-out force is also relatively low.
A connector and method of manufacture has been disclosed for the improved assembly and housing of contacts into an insulator to comprise a discrete connector. Such a connector and method of manufacture is shown and described in U.S. Pat. No. 4,184,735 assigned to the assignee of the present invention. The invention disclosed therein overcomes the disadvantages of the prior art by providing an insulative housing, which permits simultaneous loading of removable contacts from the top with relatively small push-in forces sufficient to seat the contacts therein, and yet lock the contacts into the seated configuration to establish high push-out forces. However, in that embodiment the insulative housing itself is not removable from around the contacts secured to a mounting substrate. The various considerations of "press-fitting" are also not addressed in the aforesaid disclosure, which illustrates a bowed contact mating portion.
During the past decade, the "press fit revolution" has caused the electrical connector industry to re-evaluate many of the basic concepts which resulted in the requirement that all contacts be firmly soldered in position. The press fit concept involves the forced insertion of a contact bullet region down into a plated through hole in a circuit board slightly smaller than the bullet so that the contact is held in snug, rigid engagement with the walls of the hole. The hole walls are generally formed by plating through the drilled or punched board aperture with copper and then coating the copper with a layer of tin/lead solder material. The size of the contact and the size of the hole are configured relative to one another so that the interference between the contact and the walls of the hole provide a totally reliable electrical and mechanical engagement therebetween. The school of press fit has further subdivided itself into the advocates of the solid cross section press fit region and those who urge the advantages of a compliant region. A solid contact bullet region press fitted into a plated hole moves the side walls thereof while a compliant bullet inserted into the hole theoretically elastically yields and thereby reduces the potential damage to the insides of the holes from force fit insertion. The contacts and method of the present invention are directed principally toward the fabrication of a reliable load bearing press fit shoulder above a press fit region on the contact. The paramount reason includes the initial dimensional parameter of the square wire material stock, because only a limited number of transverse dimensional variations can be imparted to wire stock by cutting or grinding. The concept of coining a square wire fabricated contact to generate a press fit region affords certain advantages over the above described methods and is disclosed in co-pending U.S. pattent application Ser. No. 174,889, filed Aug. 4, 1980. One aspect of said copending application is the provision of a method of forming press fit regions on contacts of all configurations for permitting press fit engagement by "pull home" forces. The methods and apparatus thus set forth facilitate the modification and assembly of a wide variety of contacts and connectors into press fit interconnection systems having optimized push-in/push-out features adapted for single or multi-layer boards. The transversely offset, coined region is formed in the conventional tail portion of the contact in such a manner so as to provide an optimum "push-fit" engagement within the tensile strength of the particular material under pull fit loading.
Many other advantages are obtained in a discrete insulator-contact subassembly which provides for press fitting of the contacts. Certain prior art electrical connectors have been assembled by inserting press fit contacts into the sleeves of an insulative housing and having them initially held in position by frictional interference with the side walls of the sleeves and subsequently press fitted into apertures in a mounting substrate by applying axial forces to the upper tips of the contacts. Such a connector and method of manufacture is shown respectively in U.S. Pat. Nos. 4,035,047 and 4,127,935 assigned to the assignee of the present invention. Such connectors as shown in the above referenced patents are of the metal to metal type, as opposed to a card edge connector and further include an upper contacting portion capable of withstanding and transmitting the forces required for press fitting contacts. Problems with such techniques arise whenever it is desired to form card edge connector contacts having a bellowstype interconnecting portion, a press fittable intermediate section and a removable insulator.
The advantages of the bellows-type contact may be illustrated in U.S. Pat. No. 4,094,573 assigned to the assignee of the present invention. It may be seen that the upper bellows mating portion does not permit the transfer of an axial loading force for a press fit engagement. Moreover, such connector configurations generally incorporate sophisticated securing, or latching means to hold the contact within the insulator. Such latching means do not lend themselves to the various aspects of press fitting and repairability discussed above. In particular, the prior art bellows contact does not present a configuration heretofore facilitating a press fittable contact-insulator subassembly permitting transportation of the subassembly to a remote location for press fit assembly to a mounting substrate. The method and apparatus of the present invention provides such a combination by providing a "pull-home" bellows contact having longitudinally disposed and laterally spaced alignment means and received within a pull-through insulative housing.